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Studies into how pain and breathing are connected could lead to safer pain drugs

MARY LOUISE KELLY, HOST:

When people feel pain, they tend to breathe faster. When they take an opioid to kill that pain, their breathing slows down. Now scientists think they know how pain and respiration are connected in the brain. NPR's Jon Hamilton reports that the discovery could eventually lead to safer pain drugs.

JON HAMILTON, BYLINE: Sung Han has been studying the link between pain and breathing in his lab at the Salk Institute in San Diego. But he got a real-world demonstration recently while taking a shower.

SUNG HAN: I forgot to change the temperature, and the cold water just suddenly came out and covered my entire body. And then I just - I was breathing really fast.

HAMILTON: A typical reaction to what Han calls aversive sensory information - and he thinks he knows the cause. Han's lab has identified a brain circuit in mice that appears to link the emotional experience of pain to breathing rhythm. Han says the circuit involves two populations of brain cells both found in the same small area of the brain stem.

HAN: One population regulate pain and the other population regulate breathing, and that's the reason why pain and breathing are interacting each other.

HAMILTON: They're linked together. If that's also true in people, it would help explain the mysterious connection between breathing and emotion, which has puzzled scientists for centuries. And the finding, which appears in the journal Neuron, could also have practical applications. That's because both groups of brain cells - the ones for breathing and the ones for pain - respond to opioids. Han says this is why an overdose can be fatal.

HAN: The reason why people die is just the opioid suppress the breathing.

HAMILTON: One of the scientists who helped show how opioids kill is Dr. Kevin Yackle at the University of California San Francisco. Yackle says until now, most research has focused on either the brain cells involved in pain or the ones involved in breathing.

KEVIN YACKLE: The connection between the two is still something that's very new. You know, and perhaps studies like this are some of the first examples of this.

HAMILTON: Yackle says understanding the connection could lead to a new type of opioid - one that spares the brain cells that keep us alive.

YACKLE: Maybe the molecular mechanism by which opioids silence those neurons is different than the molecular mechanism that's used by opioids to cause analgesia or pain relief.

HAMILTON: Yackle says the new study also could point the way toward better drugs to revive a person who has overdosed.

YACKLE: The only way right now to reverse all these effects is to give somebody an opioid receptor antagonist like naloxone.

HAMILTON: Also known as Narcan - the drug restores normal breathing but it can also induce withdrawal symptoms, which may lead to more drug taking and another overdose. Yackle says a drug that only restored breathing would be a better option. And he says making opioids safer should be a priority in a country where overdoses kill more than 100 people a day.

YACKLE: Opioids are the best analgesics, and so finding some way to maintain their capacity as analgesics yet get rid of these negative side effects I think is a really important goal.

HAMILTON: Though, it's one that is still years away. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.